In general, a seat slide apparatus for a vehicle includes a lower rail to be retained to a vehicle floor, an upper rail retaining a seat, the upper rail provided movably relative to the lower rail, and a lock mechanism for restraining movement of the upper rail relative to the lower rail. In the seat slide apparatus for a vehicle, a seat position in a vehicle frontward-rearward direction may be adjusted by releasing the lock mechanism from a restrained state to an unlocked state where the upper rail is allowed to move relative to the lower rail.
Furthermore, a known seat slide apparatus includes a function generally known as a walk-in function. The walk-in function brings a lock mechanism of the known seat slide apparatus to an unlocked state in accordance with an operation to knock down a seat back in a frontward direction and retains the lock mechanism in the unlocked state.
For example, a known seat slide apparatus disclosed in JP2004-122798A, hereinafter referred to as Reference 1, includes an unlock lever and an unlocked state retaining lever. The unlock lever rotationally moves in conjunction with an operation to knock down a seat back in a frontward direction to unlock a lock mechanism. The unlocked state retaining lever restrains the unlock lever from making rotational movement by engaging with the unlock lever. The unlock lever is restrained from making rotational movement at a position at which the unlock lever unlocks the lock mechanism. Accordingly, the lock mechanism is retained in an unlocked state in which the lock mechanism is unlocked. Furthermore, in the known seat slide apparatus according to Reference 1, a sensor bracket is arranged on a lower rail. In a case in which a walk-in function is operated, the sensor bracket and an end portion of an unlocked state release lever, which is integrally formed with the unlocked state retaining lever, make contact in accordance with an upper rail moving relative to the lower rail. As a result of the sensor bracket and the end portion of the unlocked state release lever making contact with each other, the unlocked state retaining lever makes rotational movement that disengages the unlocked state retaining lever and the unlock lever so that the lock mechanism is released from the state where the lock mechanism is maintained in the unlocked state.
In other words, the configuration of the known seat slide apparatus according to Reference 1 retains the lock mechanism in the unlocked state unless the upper rail moves to a position at which the unlocked state release lever makes contact with the sensor bracket. As a result, in order to adjust a seat to a desired position during sliding movement, the seat is required to move to a position where the seat is released from the state in which the seat is retained in the unlocked state first, then the seat is required to make the lock mechanism unlocked again to adjust the seat to the desired position, which is considered as a drawback.
A need thus exists for a seat slide apparatus for a vehicle, which is not susceptible to the drawback mentioned above.